Semiconductor materials are utilized in a broad range of applications including, but not limited to, logic gates, sensors, solar cells, and thermoelectric devices. These materials are typically produced using epitaxial or other crystal growth methods and serve as the backbone of modern electrical applications. Due to crystal growth techniques, the underlying semiconductor materials are most often in the form of a flat wafer that is rigid and fragile. These semiconductor wafers are processed using lithography or other methods to produce a final device. An alternative method for producing a semiconductor material is to use colloidal growth techniques to produce semiconductor nanocrystals. These nanocrystals are often grown as a suspension in a solvent and may have stoichiometries that are the same as or very similar to their traditional, epitaxial counterparts.
Recent research has focused on developing an optimal material system for thermoelectric and solar cell applications. The ideal material structure exhibits a discrete distributed density of electron states which is best formed by a nanostructured material constructed of discrete semiconductor nanocrystals. Creating this ideal material structure has proven to be a challenge because of the complexity of getting a uniform stoichiometry and morphology across the entire material. Creating chemical reactions that result in scalable, controllable, nano-sized semiconductor particles is also very difficult.
Previous attempts have included forming Bi2S3 nanocrystals, and then performing an ionic exchange with Sb2Te3 in the presence of excess Te to form BiSbTe3 nanocrystals. This method was preferred due to easy to control kinetics of the reaction and the ease of scaling the process. However, the nanocrystals synthesized according to these methods tend to have Bi-rich and Sb-rich phases within the final material. These prior methods essentially form a core of Bi2Te3 with a shell of Sb2Te3. The final material stoichiometry may match the ideal target stoichiometry, but there are nano-sized phases of different material stoichiometries within the overall material that may inhibit the thermoelectric or solar cell performance characteristics.